Changes in oxygen and carbon dioxide in the genesis of sleep bruxism: a mechanism study

Rhythmic masticatory muscle activity (RMMA), a biomarker of sleep bruxism (SB), has been associated with mild hypoxia and/or big breaths in some adults with non-sleep-disordered breathing. The purpose of this study was to investigate that concurrent oxygen and carbon dioxide fluctuations are among the physiological variables that contribute to RMMA onset.

Twelve subjects (5 female, 7 male, mean age: 43 ± 11) underwent polysomnography recording in a sleep laboratory. RMMA index and apnea-hypopnea index were calculated. Oxygen saturation (SpO₂) was estimated by finger pulse oximeter and end-tidal CO₂ (ETCO₂) by nasal airflow cannula before and after RMMA onset. Given the expected response time delay between actual arterial hypoxemia and fingertip pulse detection, we adjusted the SpO₂ desaturation onset to the onset of masseter muscle activity using a 17 s criterion based on ETCO₂ shifts.

SpO₂ was slightly but significantly lower than at baseline (max: -0.6%) in the 6-4 s before RMMA onset and significantly higher in the 6-18 s after onset (0.9%; p < 0.05). Although ETCO₂ before RMMA onset did not differ from baseline, it decreased at 8-10 s after onset (-1.7 mmHg: p < 0.05). No changes in SpO₂ or ETCO₂ in relation to RMMA onset reached a critical clinical threshold.

The mild transient hypoxia observed before RMMA onset was not associated with a change in ETCO_2. The mild and brief oxygen fluctuations before RMMA onset may reflect a physiological response that seems to have little influence on SB genesis.